In the case of an acryl based resin, because of its low cost and high transparency, it is useful as a resin for a film. However, an acrylate film that includes an acryl based resin has a problem in that since the acrylate film has the poor mechanical properties, it is insufficient to produce the acrylate film as a desired film. In order to improve this, an effort in which the acrylate film is produced by using a material that is obtained by polymerizing the resin after a soft segment is added to the acryl based resin has been made, but it is required that a film having the desirable mechanical properties is developed.
In addition, the film that is produced by using the styrene based resin is a material that shows an optical anisotropic property in which a refractive index is increased in a direction that is vertical to the alignment direction when the resin is stretched and aligned. It is known that the resin is useful to produce the film having the positive thickness retardation value (Rth) by stretching it. In addition, the styrene based resin has advantages of excellent economical efficiency and transparency. However, there are problems of insufficient heat resistance and poor mechanical properties, except that the film is produced in conjunction with costly special monomer.